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Old 02-03-2013, 11:55 AM   #1
Darth Wagon
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Member#: 269713
Join Date: Jan 2011
Vehicle:
2007 WRX Ltd. Wagon
Obsidian Black Pswirl

Default OTS map with EJ257/255 hybrid

So get comfy, it's a long one-

My stock 07 WRX with 94K miles is currently in the shop for a cylinder 4 misfire due to a blown head gasket and I'm considering replacing my short block with a factory EJ257 while everything is torn apart.

I've spent 2 weeks considering all options on the table including having my current block rebuilt with upgraded crank, rods, pistons, and bearings, or buying a factory built block, or just doing the head gasket job and leaving everything otherwise the same. I think I'm leaning towards the factory EJ257 short block option for the sake of mileage longevity. I know the factory pistons are susceptible to ringland failure but it seems like built short blocks from a tuner usually don't do the mileage that a factory one is capable of. This is my DD and I have 4 years of payments left.

As the job is finished, I will be purchasing an AP and making the change to a stage 1 map, with the intent to add the Cobb DP and CBE down the road as funds allow. I'm hoping the OTS map will lessen the likelihood of ringland failure on the new block due to the factory tune running lean.

End of cool story, now for my question. Given that using my 255 heads on a 257 block can increase compression slightly, would the OTS stage 1 ACN91 map be an issue with the slightly higher compression ratio? If money were no object, then I would obviously purchase the AP and then have a Cobb pro tuner tweak it for my specific setup. That's going to have to wait since I'm already thousands of dollars into this issue already.

Any help or advice would be great. Thanks.
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Last edited by Darth Wagon; 02-05-2013 at 02:31 AM.
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Old 02-03-2013, 07:51 PM   #2
Dillinja666
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Build your old block if you are wanting to get more power out of it down the road. Built blocks can get the same mileage as a stock block, they just normally see way more stress then a stock block gets and fail earlier.

Then I would run an AP with an OTS map to break in then have a dyno tune.
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Old 02-04-2013, 08:30 AM   #3
Cobb Tuning
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Default

Quote:
Originally Posted by Darth Wagon View Post
So get comfy, it's a long one-

My stock 07 WRX with 94K miles is currently in the shop for a cylinder 4 misfire due to a blown head gasket and I'm considering replacing my short block with a factory EJ257 while everything is torn apart.

I've spent 2 weeks considering all options on the table including having my current block rebuilt with upgraded crank, rods, pistons, and bearings, or buying a factory built block, or just doing the head gasket job and leaving everything otherwise the same. I think I'm leaning towards the factory EJ257 short block option for the sake of mileage longevity. I know the factory pistons are susceptible to ringland failure but it seems like built short blocks from a tuner are usually don't do the mileage that a factory one is capable of. This is my DD and I have 4 years of payments left.

As the job is finished, I will be purchasing an AP and making the change to a stage 1 map, with the intent to add the Cobb DP and CBE down the road as funds allow. I'm hoping the OTS map will lessen the likelihood of ringland failure on the new block due to the factory tune running lean.

End of cool story, now for my question. Given that using my 255 heads on a 257 block can increase compression slightly, would the OTS stage 1 ACN91 map be an issue with the slightly higher compression ratio? If money were no object, then I would obviously purchase the AP and then have a Cobb pro tuner tweak it for my specific setup. That's going to have to wait since I'm already thousands of dollars into this issue already.

Any help or advice would be great. Thanks.
I'm not sure of the exact difference in compression ratio with that set up, but unless it is a relatively inconsequential difference, you have to be very careful. A custom tune would be much more ideal, but if you have to run on it on an OTS map, then I would use the most conservative OTS map available, which would be the 91ACN LWG map. Then verify via wide open throttle (WOT) pulls in 3rd gear from around 2500 RPM on up (if you can do so safely). Check out our data logging video below for details. If everything looks good with multiple pulls (especially with knock correction) then you can progress up to more aggressive maps (depending on the octane gas you are using).


Bill
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Old 02-04-2013, 06:29 PM   #4
Darth Wagon
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Member#: 269713
Join Date: Jan 2011
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2007 WRX Ltd. Wagon
Obsidian Black Pswirl

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Thanks for the quick reply, Bill. The best thing we have in NorCal is 91.
I meant to include some compression estimates in my first post. From what I can find here and in some other forums, the stock WRX EJ255 block w/ stock EJ255 heads runs around 8.55:1, give or take. The STi's EJ257 block w/ the WRX's EJ255 heads is 8.78:1.

I don't know if this would be considered minimal enough for the OTS map, but for the sake of my wallet and my marriage, I'm going to have to start there and go the pro-tune route when funds allow.

Last edited by Darth Wagon; 02-04-2013 at 06:42 PM.
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Old 02-04-2013, 06:39 PM   #5
Darth Wagon
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Member#: 269713
Join Date: Jan 2011
Vehicle:
2007 WRX Ltd. Wagon
Obsidian Black Pswirl

Default

Quote:
Originally Posted by Dillinja666 View Post
Build your old block if you are wanting to get more power out of it down the road. Built blocks can get the same mileage as a stock block, they just normally see way more stress then a stock block gets and fail earlier.

Then I would run an AP with an OTS map to break in then have a dyno tune.
Thanks for the input.

I was originally going the built block route but couldn't seem to find anybody saying they got more than 50-70K miles on one. Granted, people who have gone that route do so because they are pushing a lot more power than I am planning on, but I was nervous to gamble with that kind of money.

I'm hoping to go at least 100-120K on a stage 1 tune before tearing into it again, by that time it will be paid off and I'll probably have another car to drive while I rebuild it.
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Old 02-05-2013, 08:40 AM   #6
Cobb Tuning
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Quote:
Originally Posted by Darth Wagon View Post
Thanks for the quick reply, Bill. The best thing we have in NorCal is 91.
I meant to include some compression estimates in my first post. From what I can find here and in some other forums, the stock WRX EJ255 block w/ stock EJ255 heads runs around 8.55:1, give or take. The STi's EJ257 block w/ the WRX's EJ255 heads is 8.78:1.

I don't know if this would be considered minimal enough for the OTS map, but for the sake of my wallet and my marriage, I'm going to have to start there and go the pro-tune route when funds allow.
I would be very careful since you don't have any where to really go with a less conservative OTS map since you are already on the poorest fuel quality (CA 91). I would recommend getting a protune. You can certainly drive the car around without issue if you avoid WOT or heavy throttle pulls until your protune. If you really want to run the OTS maps, then I would go with the LWG 91ACN and carefully data log to make sure everything looks good.

Bill
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Old 02-05-2013, 11:24 AM   #7
Darth Wagon
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Member#: 269713
Join Date: Jan 2011
Vehicle:
2007 WRX Ltd. Wagon
Obsidian Black Pswirl

Default

Yeah, that makes sense. I'll probably stay on the stock tune and just use the AP for data logging until I can go the pro tune route. I'll be following a fairly conservative break-in procedure anyway so by the time that's done I'll probably be ready.

Thanks for all of your help, it's services like these that made me decide to use Cobb in the first place.
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Old 02-06-2013, 08:15 AM   #8
Cobb Tuning
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Quote:
Originally Posted by Darth Wagon View Post
Yeah, that makes sense. I'll probably stay on the stock tune and just use the AP for data logging until I can go the pro tune route. I'll be following a fairly conservative break-in procedure anyway so by the time that's done I'll probably be ready.

Thanks for all of your help, it's services like these that made me decide to use Cobb in the first place.
No problem. I didn't want to convey that you absolutely must have a protune. The compression change is not huge - it is possible that you could run the OTS 91ACN map, just that you would want to carefully data log by doing multiple WOT pulls (after the break-in period) and check to make sure everything looks good. Also doing runs where knock may be more likely - such as high outside temperature, etc. You just have a more narrow window to work with (slightly higher compression ratio and poorer than average gas quality). Certainly, though, a protune would be ideal.

Bill
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